Device for the detection of excessive thread tension and thread breakage

ABSTRACT

A device for detecting the breakage of, and excessive tension in, the thread operating in knitting machinery, the device comprising a case, a first detection lever for detecting breakage of the thread, and a second detection lever for detecting excessive thread tension, both detection levers being pivotally mounted to the case. The second detection lever cooperates with a return spring attached at one end thereof to the lever and at the other end thereof to the case. The location of the points at which the spring is attached to the second detection lever and case respectively are such that the spring provides a force which resists the pivoted movement of the detection lever, such force varying by a small but uniform amount with the angle defined by the lever. The thread is applied to and supported by the second detection means. When the thread is subjected to excessive tension, the second detection lever pivots against the resisting force of the spring until it reaches an angle at which the thread escapes. The detection lever and return spring configuration is such that after the thread escapes, the return spring forces the lever back to its original position, without any need to reset it.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to knitting machinery and more particularly to adevice which detects overtension and/or breakage in thread.

2. Prior Art

Devices for detecting excessive tension and breakage of threads intextile machinery are known in the prior art. Typically, these devicesof the prior art are comprised of two detection levers pivotally mountedon a case, the first detection lever being arranged and configured todetect the breakage of thread, while the second lever is arranged andconfigured to detect excessive tension in the thread. In these knowndevices, the first detection lever includes a counterweight which, ifand when the thread breaks, causes a pivoting thereof to occur. Suchpivoting provides the indication of thread breakage. The seconddetection lever typically includes a coil or spiral spring whichresiliently maintains it in a proper position to hold the thread so longas the tension on the thread is not excessive. However, when the tensionon the thread becomes excessive, the second detection lever pivots to anangular position which enables the thread to escape therefrom beforebreaking.

The devices of the prior art have several significant limitations andshortcomings which the present invention overcomes. For one thing, inmost of the known devices, the tension of the spring used in connectionwith the lever for detecting excessive thread tension increases toorapidly as the detection lever pivots, so that very often, the threadbreaks before the lever assumes the angular position which would enablethe thread to escape. When this occurs, the operator must join togetherthe ends of the broken thread and restart the machine, causing a delayin operation. The present invention substantially precludes the breakageof thread, even relatively thin thread, due to the rapid increase ofspring tension as the second detection lever pivots.

A second shortcoming of some of the devices of the prior art resultsfrom the manner in which the spring is connected to the lever fordetecting excessive thread tension. Often, this spring is placed in sucha position that the detector lever, if it passes beyond a certainbalance point in the course of its pivoting movement, tilts suddenly toa fully open position in which it is maintained by the tension of thespring. For this reason, when over-tension in the thread is detected andthe thread escapes, it is necessary, before restarting the machine, toreset the detection lever to its closed position, in addition to theusual replacement of the thread. However, the resetting of the detectionlever is often difficult to carry out inasmuch as it is typicallylocated at a relatively great height on the knitting machine. Thus, itsresetting requires the use of manually manipulated long pole or stick(in addition to the pole or stick required to replace the thread). Therequirement for an additional pole or stick to reset the detectionlever, or the need for a specific pole or stick adapted to enable boththe replacement of the thread and the resetting of the detection leveris a significant disadvantage of these known devices. Moreover, therequirement to reset the detection lever causes a further delay in therestarting of machine operation.

BREIF SUMMARY OF THE INVENTION

The present invention is an improvement in knitting machines. It is adevice comprising a case and two detection levers pivotally mountedthereto, the first detection lever for detecting a breakage in threadand the second for (i) holding the thread, (ii) detecting excessivetension thereof and (iii) allowing the thread to escape when excessivetension is detected. The second detection lever is connected to one endof a return spring, the second end of the spring being connected to thecase. The return spring provides a force which pulls the seconddetection lever against an abutement. It is a novel feature of thisinvention that the end points of the spring are on opposite sides of animaginary straight line joining the axis of rotation of the seconddetection lever and the point at which the thread is applied to thesecond detection lever. It is a further feature of this invention thatthe spring is affixed at one of its ends to the case at a point locatednearer to the axis of rotation of the second detection lever than to thepoint at which the thread is applied thereto, and that the spring isfixed at its other end to the second detection lever at a point nearerto the point at which the thread is applied thereto than to the axisrotation of said detection lever.

Still another feature of the present invention is that the longitudinalaxis of the spring forms an angle of less than 45° with the imaginarystraight line between the axis of rotation of the second detection leverand the point at which the thread is applied thereto. Further, thelength of the spring is substantially the same as the length of theabove-described imaginary straight line.

Thus, it is a principle object of the present invention to provide adevice for detecting thread breakage and excessive thread tension withgreat sensitivity and without introducing the risk of itself causing thebreakage of the controlled thread, even very thin thread.

Another object of this invention is to provide a thread breakage andover-tension detection means which is simple to use and which does notrequire any additional resetting operation in order to place a threadthereon.

Still another object of this invention is to provide a detection leverfor detecting excessive tension in thread, arranged and configured sothat a spring force which resists its pivotal movement varies by a smallbut uniform amount with the angle defined by the lever.

One advantage of the present invention, attributable to the aforesaidfeatures and objects, is that it reduces the friction of the thread onthe second detection lever and also the risk of the shag of the threadforming knots and accumulating where the thread is supported by saidlever.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the present invention is illustrated in theaccompanying drawings, it being understood that the invention is notlimited to the particular features therein shown.

FIG. 1 is a side view of an embodiment of the present invention.

FIG. 2 is a plan view of the device shown in FIG. 1.

FIG. 3 is a cross-sectional view taken along lines A--A, of the deviceshown in FIG. 1.

FIG. 4 is a broken away side view into the case of the device shown inFIG. 1.

FIG. 5 is a front perspective view of the device shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises, in general, a case 1, a first detectionlever 2 for detecting the breakage of a thread 13, and a seconddetection lever 3 for detecting excessive tension in the thread 13.

In addition, affixed to the case 1 are a plate 4 and an intermediateplate 5. Plate 4 enables the invented device to be secured to anadequate supporting means on the knitting machine at locating hole 4₂.Plates 4 and 5 form, with their leading edges, 4₁ and 5₁ respectively,an inclined ramp to enable the thread 13 to be introduced into thedetection lever 3.

The detection lever 2 for detecting thread breakage is fixed to a firstspindle 6 mounted pivotally on the case 1. Spindle 6 is integral with athreaded extension 7 onto which a head 8 is screwed adjustably so as toform a counterweight for detection lever 2.

Inside the case 1, a metal stud 9 is fixed on the spindle 6. During thepivoting motion of the detection lever 2, stud 9 can come into contactwith a resilient metal blade 10, likewise located within the case 1. Thestud 9 and the blade 10 serve as contact points in a simple electriccircuit, connecting a source of electrical energy to a socket 12containing a bulb 11. When the thread to be controlled 13 is placed onthe second detection lever 3, beyond the edges 14 of the plates 4 and 5,the thread 13 maintains the first detection lever 2 in position.However, if thread 13 should break, the counterweight 8 causes thedetection lever 2 to pivot about spindle 6, thereby causing the stud 9to contact the metal blade 10 and the bulb 11 to be supplied withelectrical current. The turning on of the bulb 11 provides a visualsignal indicating that there is a failure in the thread feed of themachine. Moreover, as seen in FIG. 4, a resistor 15 is placed inparallel with the bulb 11, causing the machine to stop when the thread13 breaks, even if the bulb is damaged.

On the case 1, the second detection lever 3 is also pivotally mounted bymeans of a spindle 16. Detection lever 3, which detects over-tension inthe thread 13, is comprised of a plate, preferably of plastic material,formed in the general shape of a U, as shown particularly in FIGS. 2 and5. Detection lever 3 is mounted pivotally on the spindle 16 close to theends 3₁ and 3₂ of the arms of the U. The curved portion 3₃ of the Ushaped plate forms, together with the arms thereof, a protective housingwhich prevents the accumulation of shag from the thread 13. The thread13 is supported on the upper edge of the plate in a hollow provided forthat purpose, as shown in FIG. 1. In addition, on the upper edge of theplate forming the second detection lever 3, and more particularly, inthe hollow in which thread 13 comes to bear, a metal retaining ring 26is provided in order to facilitate the sliding movement of the thread 13and thereby avoid the build-up of shag around this ring. The ring 26 isaffixed to the edge of the U-shaped plate by gluing. It should be noted,in addition, that according to this invention, the pivoting spindle 16is substantially co-planar with the edge of the hollow on which ring 26is affixed, as seen most clearly in FIG. 5.

The second detection lever 3 is normally maintained against an abutment17 by the force of a spring 19. Abutment 17 is disposed under the edgeof a member 18 which is affixed to plate 4 and generally perpendicularthereto. The spring 19 is secured to the case at one of its ends bymeans of a stud 20 and to the detection lever 3 at its other end bymeans of a second stud 21. Stud 21 is placed off center on a knob 22which is rotatably mounted on the plate comprising detection lever 3.Consequently, rotation of the knob 22 in one direction or the otherenables the length of the spring 19 to be adjusted and, thereby, alsothe return force which it exerts on detection lever 3.

The location of stud 20, i.e., the point of attachment of one end ofspring 19 to case 1, is above the imaginary line 16-13 joining thespindle 16 to the thread 13, when the latter is in place in detectionlever 3. On the other hand, the location of stud 21, i.e., the point ofattachment of the other end of spring 19 to the detection lever 3 isbelow line 16-13. In addition, as is seen in FIG. 1, the location ofstud 20 is situated closer to the pivoting spindle 16 of the detectionlever 3 than to the point at which the thread 13 is applied thereto,while, in contrast, the location of stud 21 is situated closer to thepoint at which the thread 13 is applied to the detection lever 3 than tothe pivoting spindle 16 thereof.

In addition, according to the invention, the length of the spring 19 issubstantially equal to the distance between the spindle 16 and the pointat which the thread 13 is applied to the detection lever 3. Because thisdistance is relatively great, it is possible, by means of knob 22, toadjust the tension of the spring accurately so that the detection lever3 will resist what is considered to be normal tension in the thread 13and begin to pivot when the tension exceeds this normal level. Moreover,because of the manner in which the ends of the spring 19 are attached tothe case 1 and the detection level 3, and because of the great length ofthe spring, there is substantially no vibration of the detection lever3. Such vibration would be detrimental to the effective control of thefeed thread of a knitting machine.

In addition, according to this invention, in order to increase theprecision with which excessive tension in a thread 13 is detected, thelongitudinal axis of the spring 19 forms, with the imaginary straightline 16-13 passing through the spindle 16 and the point at which thethread 13 is applied to the detection lever 3, an angle a. By virtue ofthe fact that spring 19 is attached at one end thereof near the spindle16 and at its other end near the point at which the thread 13 is appliedto the detection lever 3, the angle a remains less than 45°. Thus, onlya relatively small component of the pulling force of spring 19 is in adirection which tends to force the detection lever 3 to its highposition against the abutment 17 (i.e., sine a). Moreover, because ofits length and position, the spring 19 is stretched only slightly whenthe detection lever 3 is driven pivotally, thereby producing only aslight increase in the spring's pulling force. By virtue of thisconstruction, as the detection lever 3 due to excess tension of thethread 13, only a relatively small small component of the slightlyincreasing pulling force of spring 19 is applied as a return or counterforce. Furthermore, inasmuch as the angle a is less than 45°, thecomponent of the pulling force is relatively uniform or linear. Thus, asthe detection lever 3 pivots, a uniformly and gradually increasingreturn force is applied thereto, tending to restore it to its highposition.

It should also be pointed out that the pivoting spindle 16 of thedetection lever 3 is placed in a way such that the imaginary straightline 16-13 forms, with the plane in which the thread 13 is included, anangle b having a maximum value of 90°. Thus, when the detection lever 3begins to pivot due to the force attributable to over tension in thethread 13, the component of the force of the thread in a directiontending to force the detection lever 3 downward decreases constantly.This is because said component of the thread tension is a function ofsine b and the angle b decreases from a maximum of approximately 90° asthe detection lever 3 pivots.

In operation, when the detection lever 3 assumes a sufficiently sharpangle (see broken lines in FIG. 1), the thread 13 slides on theretaining ring 26 and escapes therefrom; the detection lever 3 thenrises again to its initial position against abutment 17 as a result ofthe force exerted by the return spring 19. In addition, once the thread13 has escaped from detection lever 3, detection lever 2 also is freed.It then tilts due to the action of its counterweight 8, resulting inelectrical contact being made between stud 9 and metal blade 10 and,consequently, in the lighting up of bulb 11 and the stopping of themachine.

It is obvious that the invention is not limited to the examples of itsembodiment herein above described and illustrated. If necessary, otherforms and methods of embodiment can be envisaged without departing fromthe scope of the invention.

What is claimed is:
 1. A device for detecting the breakage of, and excessive tension in, the thread operating in a knitting machine comprising:a. a case; b. a first detection lever pivotally mounted to said case, said first detection lever being arranged and configured to detect the breakage of said thread; c. a second detection lever pivotally mounted to said case, said second detection lever being arranged and configured to slidably support said thread; and d. a spring means having first and second ends, said first end thereof being connected to said case at a first point and said second end thereof being connected to said second detection lever at a second point thereon, the return force of said spring tending to maintain said second detection lever against an abutment, said first and second points being situated on opposite sides of an imaginary straight line joining the axis of rotation of said second detection lever and the point at which said thread engages said second detection lever, said first point being situated nearer to the axis of rotation of said second detection lever than to said point at which said thread engages said second detection lever, and said second point being situated nearer to said point at which said thread engages said second detection lever than to the axis of rotation of said second lever the length of said spring being approximately equal to the distance between the axis of rotation of said second detection lever and said point at which said thread engages said second detection lever,whereby, said second detection lever is responsive to excessive tension in said thread by pivoting about its axis of rotation and against the return force of said spring until said thread escapes thereform.
 2. A device for detecting the breakage of, and excessive tension in, the thread operating in a knitting machine comprising:a. a case; b. a first detection lever pivotally mounted to said case, said first detection lever being arranged and configured to detect the breakage of said thread; c. a second detection lever pivotally mounted to said case, said second detection lever being arranged and configured to slidably support said thread, the axis of rotation of said second detection lever being substantially co-planar with the edge of said second detection lever on which said thread is slidably supported; and d. a spring means having first and second ends, said first end thereof being connected to said case at a first point and said second end thereof being connected to said second detection lever at a second point thereon, the return force of said spring tending to maintain said second detection lever against an abutment, said first and second points being situated on opposite sides of an imaginary straight line joining the axis of rotation of said second detection lever and the point at which said thread engages said second detection lever, said first point being situated nearer to the axis of rotation of said second detection lever than to said point at which said thread engages said second detection lever, and said second point being situated nearer to said point at which said thread engages said second detection lever than to the axis of rotation of said second detection lever,whereby, said detection lever is responsive to excessive tension in said thread by pivoting about its axis of rotation and against the return force of said spring until said thread escapes therefrom. 